1. Field of the Invention
The present invention relates to methods and systems for pumping and manipulating liquids in microscale, and particularly to methods and systems based on electrowetting principles.
2. Description of the Related Art
Mechanical micropumping systems may use various actuation mechanisms including piezoelectric, thermal, shape memory alloy, and electrostatic actuation systems. Such methods and systems employ moving parts which result in a system of diminished reliability, increased power consumption, or high operating voltage.
Direct micropumping methods and systems may employ actuation based upon principles such as electrophoresis, electroosmosis, magnetohydrodynamic, and thermally-induced surface tension. An electrophoresis based system is limited because it requires that the operating liquid contains ionic particulates. In addition, electrophoresis and electroosmosis approaches require high voltage an a high energy dissipation and operate at low speed. Magnetohydrodynamic and thermally-induced surface tension mechanisms require relatively high power to operate as well.
The area of micropumping is directed at moving very small volumes of liquid, typically within a single conduit. Ideally, a more advanced micropumping method and system would allow more complex manipulation of the liquid, such as “digitizing” a liquid (separating and manipulating increments of liquid) in very small volumes (as small as sub-picoliter). Complex manipulation would allow for mixing and moving liquid in a microfluidic matrix or circuit. However, none of the developed techniques for micropumping allow for such complex picoliter manipulation of the operating liquid.
Electrowetting is a principle whereby the surface wetting property can be modified between the hydrophobic and hydrophilic states using an electric field. The surface can be hydrophobic conductive layer or conductive layer covered with hydrophobic dielectric film. A droplet of liquid can bead or spread on the surface depending on the surface state. A liquid lens with an adjustable focus has been developed using this principle, however, there has been no application to micropumping.
There is a need for micropumping methods and systems which operate without moving mechanical parts. There is further a need for such systems and methods which operate at relatively low power and voltage and achieve a relatively high speed. There is still further a need for such methods and systems which function without requiring ionic particulates in the operating liquid. Finally, there is a need for methods and systems which will enable complex manipulation of sub-microliter liquid volumes. The present invention meets all of these needs.